The pay scale is going to be tough. Looking quickly through the top bounties, none of them are really student level. Issues that are truly good for beginners or someone unfamiliar with the codebase in any moderately popular open source project usually get scooped up immediately for resume building.
I can see this as being useful for abandoned projects, or as a way to promote something new. It's a much better signal that the ticket is actually meaningful and impactful than a GitHub tag.
Whether that is enough to get past psychological barriers behind transactions, I don't know. I do like the "buy the author a coffee or two" mentality of support, which I think does remove some of the transaction aspect of it. Not sure if this is what Rysolv was going for -- it feels a bit more formal.